In theory, bearing materials operating with full-film lubrication should never touch their mating parts. However, under actual operating conditions, bearing materials do, and in some cases must, contact their mating surfaces. Hence, successful use of a bearing material depends on matching its properties to the demands of the application. Performance characteristics of conventional bearing materials include the following:
A. Compatibility -- a measure of the antiweld and anti-scoring characteristics of a bearing material when operated with a given mating material. The friction developed at points of contact between the bearing material and its mating part can produce localized welding, thereby causing a seizing or scoring. Thus, a good bearing material will not weld easily to its mating part. PA1 B. Conformability -- ability to compensate for misalignment and to conform to other geometric errors. Soft metals with a low modulus of elasticity exhibit excellent conformability characteristics. PA1 C. Embeddability -- ability to absorb dirt and foreign particles so as to avoid scoring and wear. PA1 D. Load Capacity -- expressed in pounds per square inch, it is a measure of the maximum hydrodynamic pressure which a material can be expected to endure. PA1 E. Fatigue Resistance -- ability to perform under load changes without cracking or chipping.
Babbitts (80% to 90% tin, about 3 to 8% copper and 4 to 14% antimony), bronzes and other copper alloys, and aluminum alloys are presently being used as bearing materials to satisfy the widely varying requirements of particular applications. However, when selecting a particular bearing material, the performance characteristics theoretically desired will have to be compromised since no bearing material is equally good with respect to all operating requirements. For example, an aluminum bronze may be chosen for its high load bearing capacity and low wear rate even though it has poor compatibility, embeddability and conformability relative to a leaded bronze, simply because the leaded bronze will not carry a load at all.
Other material used at one time or another as bearing materials include cadmium, silver, cast iron, steel, phenolics (composite materials consisting of cotton fabric, asbestos, or other fillers bonded with phenolic resin), carbon-graphite, rubber, cermets and ceramics. Conventional cermets are composed of a high volume fraction of hard particles (oxides, carbides, etc.), almost always greater than 50% and usually greater than 85%, have a high bulk hardness, are usually brittle and have very poor conformability, impact resistance and embeddability. Thus, cermets are used in bearing applications only when a very precise positioning is required since they are very expensive, difficult to machine, and have to be individually custom produced.
In recent years, plasma deposited, flame sprayed and detonation gun coatings have been used to produce bearing materials and to repair conventional wrought and cast alloy bearings. Not only do these coatings meet the requirements of the original material, but their wear rates have been found to be lower than the conventional materials. The present invention is directed to an improvement over the current generation of plasma deposited, flame sprayed, or detonation gun wear-resistant bearing coatings, and specifically to a bearing material so produced in which hard particles are intentionally added to ductile metal matrices.